[Select_Answers]WS1_Evolution_Fa23

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Biology 1B Study Sleuth Evolution Worksheet 1 (Lecs 3-7) Fall 2023 For the schedule of future Study Sleuth sessions, please see weekly email announcements & the OH Calendar on bcourses. All answers can be found in your lecture material. Warm-Up Question 2. (UPDATED WITH PROFESSOR MARSHALL’S INPUT) Build a tree Looking at the following (made up) DNA matrix, circle/highlight in one color the potential synapomorphies (shared character states not shared with the outgroup). Then box/highlight in another color the autapomorphies (evolutionary innovation present on only one branch of a cladogram, that do not help infer or determine evolutionary relationships). Finally, draw the most parsimonious phylogeny tree. (Note: ignore the branch lengths) Source: Professor Marshalls Outgroup: AATT CTGC AGAG CTAC Dolphin: GATT CTGC AGAA TTAC Goldfish: AGTT TTGC AGAA CCAC Tuna: AGTT TTGC AGAA CTAT Starfish: AATC CTGT GGAG CTAC 4. Monophyly, Polyphyly, Paraphyly For the trees below, explain whether each shaded group is monophyletic , polyphyletic , or paraphyletic . [Hint: use the definition of each type of group]

A monophyletic taxon is one that includes a group of organisms descended from a single ancestor. Mammals are monophyletic. A polyphyletic taxon is composed of unrelated organisms descended from more than one ancestor. It does not include the common ancestor of all members of the taxon. “Marine mammals” is a polyphyletic group because it includes distantly related species such as whales, manatees, and seals.

A paraphyletic taxon is one that includes the most recent common ancestor, but not all of its descendents. Reptiles are a paraphyletic group. Follow-up question 1: what is the role of an outgroup? (lec 6) - For differentiating plesiomorphy (primitive/ancestral character state) & apomorphy ( derived ancestral state) . - plesiomorphy & apomorphy on a tree always has to be identified/understood in a context (i.e. “the xx character state in xx taxon is plesiomorphic/apomorphic relative to yy taxon”) Follow-up question 2: does the branch length in the diagram above have a meaning? (lec 7) - Yes because there’s a time scale at the bottom (which means it’s a phylogeny). - Branch lengths are proportional to time - If we get rid of the time scale then it becomes either a phylogram or a cladogram. (without the time scale you can’t tell phylogram and cladogram apart just by how the diagram appears - unless the question specifies it for you.) - Phylogram: branch length still has meaning (proportional to the strength of support)

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- Cladogram: no meaning! Part 3: Practice Questions Directions : Work on the following practice questions to get ready for your exam with the peers around you. 1. Link each of the following examples to a type of natural selection: (i) The number of fruit set of a plant is being selected. The mean trait value for the number of fruits borne on the branch is selected to become higher over time. Directional selection (ii) The clutch size of a species of bird is being selected. Birds that lay too many eggs have an increased chance of losing offspring to starvation, and birds which lay too few have a decreased chance of these birds surviving and passing their genes on. Stabilizing selection (iii) The beak size of finches in the Galapagos is being selected. One fitness peak appears for relatively large billed birds and another peak for relatively small billed birds. Disruptive selection (note that all examples above are selection acting on a trait, not on a gene or allele) Questions 2-4: Baum, D. A. (2005). EVOLUTION: The Tree-Thinking Challenge. Science , 310(5750), 979–980. doi:10.1126/science.1117727 2. By reference to the following tree, which of the following is an accurate statement of relationships?

a. A crocodile is more closely related to a lizard than to a bird b. A crocodile is more closely related to a bird than to a lizard i. B is the correct answer. The most recent common ancestor of a crocodile and a bird is at node x whereas the most recent common ancestor of a crocodile and a lizard is at the “deeper” node, y. If you picked “a”, you might be reading along the tips of the cladogram. c. A crocodile is equally related to a lizard and a bird d. A crocodile is related to a lizard, but is not related to a bird 3. Which of the four trees depicts a different pattern of relationships than the others? Circle this tree. Choice c is the correct answer. In all the other trees C is more closely related to E and D than to B. In cladogram c, C is more closely related to B than to E or D.

4. In the below tree, assume that the ancestor had a long tail, ear flaps, external testes, and fixed claws. Based on the tree and assuming that all evolutionary changes in these traits are shown, what traits does a sea lion have? a. Long tail, ear flaps, external testes, and fixed claws b. Short tail, no ear flaps, external testes, and fixed claws c. Short tail, no ear flaps, abdominal testes, and fixed claws d. Short tail, ear flaps, abdominal testes, and fixed claws i. D is the correct answer. Tracing up from the ancestor to sea lions, one sees that the only changes are in the tail length and testes position. For the other traits, they have retained the ancestral condition. e. Long tail, ear flaps, abdominal testes, and retractable claws

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For your own practice, use the following link for more advanced phylogenetic questions! https://www.ebi.ac.uk/sites/ebi.ac.uk/files/content.ebi.ac.uk/materials/2014/140602_prague/tree_thinkin g_tests.pdf 5. About 13 different species of finches inhabit the Galápagos Islands today, all descendants of a common ancestor from the South American mainland that arrived a few million years ago. Genetically, there are four distinct lineages, but the 13 species are currently classified among three genera. The first lineage to diverge from the ancestral lineage was the warbler finch (genus Certhidea). Next to diverge was the vegetarian finch (genus Camarhynchus), followed by five tree finch species (also in genus Camarhynchus) and six ground finch species (genus Geospiza). If the six ground finch species have evolved most recently, then which of these is the most logical prediction? a. They should be limited to the six islands that most recently emerged from the sea. b. Their genomes should be more similar to each other than are the genomes of the five tree finch species. c. They should share fewer anatomical homologies with each other than they share with the tree finches. d. The chances of hybridization between two ground finch species should be less than the chances of hybridization between two tree finch species.

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